1. Field of the Invention
The present invention relates generally to a control circuit for signal transmission, and more particularly is directed to a control circuit for signal transmission preferred for use with a sound volume adjustment circuit and so on.
2. Description of the Prior Art
In the case where a prior art control circuit for signal transmission is employed in, for example, a sound volume adjusting circuit, since the control circuit uses generally a variable impedance element such as a bipolar transistor, an FET or the like, its control for signal transmission in amount must be carried out with a small amount of signal amplification and, in addition thereto, there is proposed a problem of distortion factor in view of the current-voltage characteristics of the element. As a result, it may become difficult that the dynamic range for the signal control can not be made wide. In general, it is desired that the dynamic range of an input signal is wide, the gain is linear for a control voltage and that the distortion factor is low for both an audio signal and a video signal.
However, since the variable impedance element has a saturation region for its voltage-current characteristics as well known, it is impossible to make its dynamic range wide and produce an output signal with a low distortion factor.